The dissolved chemical load of runoff - i.e. discharge of dissolved mass from terrestrial environments to streams, groundwater and the oceans - is important for its relationship to nutrient retention and loss in ecosystems, quality of aquatic and marine coastal habitats, and long-term climate control exerted by the ocean-atmosphere system. Vascular plants promote dissolution of primary minerals, or chemical weathering, to meet their nutritional requirements for growth; this plant-driven weathering has long been understood to affect the chemistry of soil water and the chemical loading of runoff. This research will experimentally investigate the mechanisms by which rooted plant growth affects soil water chemistry and the hydrologic loss, in runoff, of mineral-derived elements from watersheds. Previous work by us on experimental ecosystems at Hubbard Brook indicates that pine tree growth reduces both soil-water concentrations of base cations in the rooting zone, and the discharge of these cations in drainage water, relative to controls. This research is designed to investigate how, and under what conditions, mineral-to-root chemical transport is isolated from soil water and "protected" from hydrologic loss. It is hypothesized that this phenomenon is a feature of root-to-mineral attachment which occurs during plant growth. It is specifically hypothesized that ectomycorrhizal fungi and their hyphal networks function as root-to-mineral conduits which facilitate the hydrochemical control observed by us at Hubbard Brook. The hypothesis will be tested by replicated growth experiments in the laboratory and in greenhouses. The experiments will isolate fungal and fungi-root-plant effects on solution chemistry and loss in drainage from hydrologically, chemically and ecologically simple systems. Additionally, base cations will be tracked from their sources at mineral surfaces into fungal and plant tissue and into drainage. Broader impacts of this research include participation of high school and undergraduate students, particularly women, in data collection and interpretation via coursework and part-time jobs; dissemination of findings via interdisciplinary forums and the world wide web; and improvement of our understanding of long-term ecosystem sustainability and controls on the partitioning of sequestered atmospheric CO2 into short-term and long-term storage.
